Simian Virus tumor (T) antigen will be compared to the adeno-SV40 hybrid T antigen with respect to single and double strand DNA binding, site specificity and catalytic activities. The poly dT stimulated ATPase activity of T antigen will be defined in terms of the minimum size of the poly dT molecule required for optimum activation of the ATPase activity. The high affinity binding of poly dT to the T antigen will also be measured. The relation of the ATPase activity of T antigen to its role in the initiation of DNA synthesis will be examined. Attempts will be made to assay "in vitro" initiation of SV40 viral DNA in the presence of purified T antigen, host polymerases and other factors required for eucaryotic DNA synthesis. Attempts will be made to convert transformed cells to normal cells by competing T antigen off cellular DNA and onto poly dT or other high affinity binding single strand DNA species.